Slower drainage on its own is rarely an emergency. A kitchen line that used to empty in ten seconds and now takes thirty is usually carrying buildup on the pipe wall rather than a full blockage, and that is the stage where cleaning is cheap and effective. What changes the picture is a second symptom appearing somewhere else in the house around the same time: a gurgle from a different fixture, water rising in a tub when the washer drains, or an odor near a floor drain that was not there last month. Any of those alongside a slow line points at the shared line further down the system, not just one branch.
On municipal sewer, that combination usually points at the main line, not just the fixture you noticed first. On a septic system west of University Drive, it can instead mean the tank connection itself. A camera settles which one it is before we recommend anything.